-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
1/30
Networking Basic Concepts
Computer Networks
A communication system for connecting computers /
hosts.
Better connectivity
Better communication
Better sharing of resources Bring people together
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
2/30
Types of computer networks
Geographical Span
Connects hosts within a relatively
small geographical area. Same room
Geographical Span
Hosts may be widely dispersed
Across the campuses Across cities countries / countries /
Local Area Network Wide Area Network
Same building
Same campus
Speed
Faster
Typical Speed is 10 Mbps to 10 Gbps
Cost Cheaper
Ownership Issue
Physical transmission media
continents
Speed
Slower
Typical Speed is 64 Kbps to 8 Mbps
Cost Enterprise
Ownership Issue
Physical transmission media
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
3/30
Types of computer networks
Communication
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
4/30
Circuit Switching
A dedicated path is required between two stations
A path follows a fixed sequence of intermediate links
A logical channel gets defined on each physical link
Dedicated to the connection
FB
A
E
D
GC
H
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
5/30
Circuit Switching (contd.)
In Circuit Switching three steps are required for
communication:-
Connection establishment
Required before data transmission
Data transfer
Can proceed at maximum speed
Connection termination
Required after data transmission is over
For deallocation of network resources
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
6/30
Circuit Switching (contd.)
Drawbacks:-
Channel capacity gets dedicated during the entire
duration of communication
Acceptable for voice communication
Very inefficient for bursty traffic
There is an initial delay
For connection establishment
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
7/30
Packet switching
Modern form of long distance data communication
Network resources are not dedicated
A link can be shared
The basic concept remained the same
Widely used for long distance data communication
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
8/30
Packet switching (contd.)
Data are transmitted in short packets (Kbytes)
A longer message is broken up into smaller chunks
The chunks are called as packets
Ever acket contains a header
Relevant information for routing, etc
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
9/30
Packet switching (contd.)
Message
H H H
Packets
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
10/30
Packet switching (contd.)
Packet switching is based on stored-and-forward
concept
Each intermediate network node receives whole packet
Decides to route
Forwards the packet along selected
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
11/30
Packet switching (contd.)
Advantages
Link can be shared so link utilization better
Suitable for computer generated traffic
Typically bursty in nature
Buffering and data rate conversion can be performed
easily
Some packets given priority over others if desired
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
12/30
Packet switching (contd.)
How are the packets transmitted?
Two alternative approaches
1. Virtual circuits
2. Data rams
The abstract network model is same
FB
A
E
D
GC
H
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
13/30
Virtual circuit approach
Similar to the concept of circuit switching
A route is established before packet transmission starts
All packets follow same path
The links com risin the ath are not dedicated
Different from circuit switching in this respect
Analogy
Telephone system
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
14/30
Virtual circuit approach (contd.)
How it works?
Route is established a priori
Packet forwarded from one node to the next using
stored-and-forward scheme n y virtua circuit num er nee to e carrie out y
the packet Each intermediate node maintains a table created during
route establishment
Used for packet forwarding
No dynamic routing decision was taken by intermediatenodes
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
15/30
Datagram approach
Basic concept
No route is established before hand
Each packet is transmitted as an independent entry
Does not maintain an histor
Analogy Postal system
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
16/30
Datagram approach (contd.)
Every intermediate node has to take routing decision
automatically
Makes the use of routing table
Every packet must contain source and destination address
Problems:-
Packets may be deliver out of order
If the node crashes momentarily, all of its queued packets
are lost
Duplicate packets may also be generated
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
17/30
Datagram approach (contd.)
Advantages:-
Faster then virtual circuit approach for smaller number
of packets
No route establishment and termination
More flexible
Packets between two host may follow different path
Can handle the congestion link
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
18/30
Comparative study
Three types of delays must be considered:
1) Propagation delay
Time taken by the data signal to propagate from one
2) Transmission delay
Time taken to send out packet by a transmitter
3) Processing delayTime taken by node to process the packet
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
19/30
Circuit switching
After initial circuit establishment data bits are sent
continuously without any delay
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
20/30
Virtual circuit Packet switching
Call request packet sent from source to destination
Call accept packet returns back
Packets sent sequentially in pipelined fashion
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
21/30
Datagram Packet switching
No initial delay
The packets are sent out independently
Many follow different paths
- -
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
22/30
Layered network architecture
Open Systems Interconnection (OSI) reference model
Seven layer model
Communication functions are partitioned into
Systematic approach to design
Changes in one layer should not require changes in
other layer
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
23/30
The 7 layer OSI Model
Application
Presentation Host to host
physical
Session
Transport
Network
Data Link
Point to point
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
24/30
Layer function
Physical layer
Transmit row bit stream over physical medium
Reliable transfer of link over point to point link
Network layer Establishing, Maintaining and terminating connections
Routes the packet through point to point link
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
25/30
Layer function (contd.)
Transport layer
End to end reliable data transfer
With error recovery flow control
Manages the session
Presentation layer
Provides data independence Application layer
Interface point for user application
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
26/30
How data flows in 7 layer model?
Session
Application
Session
Application
presentation presentation
physical
Transport
Network
Data Link
physical
Transport
Network
Data Link
S DA B
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
27/30
Internetworking Devices
Hub
Extends the span of single LAN
Bridge / layer-2 switch
Works at data link layer level
Router / Layer-3 switch
Connects any combination of LAN and WANWorks at network layer
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
28/30
Campus network schematic
Department
NetworkDepartment
Network
Backbone
Backbone n/w: Fast Ethernet, FDDI, ATM, Gigabyte Ethernet
DN: Switched Ethernet, Bus based Ethernet
Department
Network
Department
Network
Network
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
29/30
Connecting computer to departmental
network
Requires NIC
Connection through
switch or hub
Backbone network
shown
C C C
HUBHUB
Ethernet switch
-
8/4/2019 Networking Basic Concepts Lecture 2 Web Technology
30/30
Connecting to outside world
Radio link
Satellite
Antenna
Institute
network
Router
Modem Telephone line
leased line